1. Field of the Invention
This invention relates generally to the art of controlling and suppressing the radar cross-section and signature of a space vehicle, particularly an orbiting satellite vehicle, either for the purpose of preventing its detection by ground based radar detection systems or modifying its radar signature to resemble another space vehicle, such as a decoy. The invention relates more particularly to a space vehicle antiradar screen structure having a novel crossed skirt configuration.
2. Prior Art
At the present state of development of the space vehicle detection art, the most important vehicle observable to be controlled is radar cross-section or signature. This is particularly true of orbiting satellite vehicles whose repeated passes around the earth allow ample time for radar signature analysis and possible ultimate identification of the satellite. A variety of techniques have been devised for controlling and reducing radar cross-section of a space vehicle in a manner such that the vehicle may be effectively decoyed. Such an antiradar device or antiradar screen must either completely deny detection of the space vehicle by search radar or reduce and modify the radar cross-section of the vehicle to permit employment of other aids, such as decoys, to confuse and delay final identification.
A proper signature match between target vehicle and decoys without modification in the target signature would require the external configuration of the decoys to substantially duplicate that of the target vehicle. In most cases, for example, the target vehicle has a characteristic fine structure of large magnitude in its radar signature which varies with frequency, polarization, and radar look angle. Duplication of this signature with a decoy would require a decoy of the same size and shape as the target vehicle, which is often impractical. As a consequence, the most effective method of shielding a target vehicle is that wherein the radar signature of the vehicle is modified to a simplified, reduced magnitude form and the vehicle is accompanied by a swarm of decoys having essentially the same radar signature as the screened target vehicle so as to cause confusion and delay in detection.
A decoy which may be used in conjunction with the signature modifying device of this invention is disclosed in applicant's copending patent application Ser. No. 04/591,395, filed Oct. 28, 1966 and entitled "Radar Target Simulator (U)" now abandoned.
U.S. Patent No. 3,233,238 discloses an antiradar screen structure for reducing radar reflection from a space vehicle. This screen structure has a cone-like shape which completely covers the vehicle and can reduce the radar reflection area to approximately a square centimeter, depending upon the frequency of the illuminating radar, the angle of the cone apex, and the reflections due to first or second order discontinuities of the vehicle's surface structure. To utilize this type of screen on an elongated vehicle body, would require a cone with a major diameter greater than the length of the vehicle which in turn would make the cone quite large in length and width.
Copending applications Ser. Nos. 04/593,233 and 04/721,513 disclose improved antiradar screens in the form of a plurality of overlapping (osculating) biconvex lenses. A line tangent to the edges of these lenses determines the contour of an arcuate keel edge of the screens. A search radar whose energy is striking this contoured edge in the plane which passes through the edges and centers of the lenses can detect only a cross-section of conductive material above the detection threshold of the radar. The cross-section of each of the lenses is chosen to be below such detection threshold. The screen is otherwise shaped such that incident radiation striking the screen outside of the edge plane also encounters a cross-section which is below the detection threshold of the radar. This is accomplished by maintaining the angle formed by the juncture of the surfaces of the screen, at the keel edge, below a value which is determined by the type of radar used and the vehicle distance from the radar.
An antiradar screen such as that just discussed must be stowed in the vehicle during launch and deployed to its operational configuration after orbit is achieved. Stowage and deployment of the screen may be accomplished in various ways. By way of example, the screen structure of copending application Ser. No. 04/593,233 is deployed in orbit by inflation of a tubular frame structure supporting the conductive skirts of the screen.